Our 2010 seedlings in half gal pots spent their first winter along east foundation of house covered with chopped leaves; about 90% died.
They didnt get enough water in that location. Make sure your seedlings dont get too dry.

They are supposed to be very hardy, so I'm guessing being dry may have been the cause. Anyways there is residual snow from christmas until usually the middle of March here so I really doubt dryness will be an issue.

My plan is to use either leaf bags, dried leaves with a tarp over them or just dried leaves since the snow insulates pretty well. I am aware that with most plants, their first winter is their toughest, especially if they are growing in pots.

Were the pots buried into the ground at all? If you left the pots simply sitting on top of the soil without burying them into the ground, that will cause the root balls to freeze which restricts the water to the plant. The only exceptions I've seen are fruit trees, blueberry plants or alliums which don't seem to mind getting their roots frozen solid.

No, pots were not buried.
Many of this years seedlings in half gal pots are buried in garden and covered with chopped leaves. We will see what happens.

I have my potted TP seedling buried already so all they need is a layer of leaves. I also plan on putting a small layer over the TP seeds that might germinate next year, and I have all kinds of tarping material which will definitely help out.

I'm guessing based on my exp with other potted plants that letting benefit from the warmth of the soil temperature is very important and anything used for protection on top of that is more like icing on the cake, but I'm playing it safe for 1st year TPs as these guys are worth a lot. A benefit with starting from seedlings is that they don't rely on a nurse root in comparison to a grafted plant.

I planted 2 tree peonies in my zone 4 garden at my last house about 2 years ago..in the ground, no winter protection, except snow. They both bloomed last year,
they're pretty hardy.
heather

The TP seedlings keep on sprouting at a steady rate, but I do get a bit scared when the forecast calls for lower teens tomorrow night. I think the 1 year old ones which already have a woody stem should be fine however the new ones which happen to still be red and soft with a well developed leaf already look very vulnerable to getting killed by cold spells.

The good thing is that by Tuesday, it looks like we will see temperatures stay well above freezing, maybe for good so many more seeds can sprout without the fear of losing them.